A few years ago in driving rain at the end of long taxi-queue at Belfast City Airport, I bumped into a senior member of the DUP a few days after the party won the Stormont Assembly elections in 2003.

"Paisley-ism was all about saying no"

I congratulated him on his own success and said flippantly that I imagined that it had set back the chances of power-sharing by decades.

He smiled and said: "I wouldn't underestimate Ian Paisley's desire to be first minister of Northern Ireland."

It seemed fantastically improbable. Paisley-ism was all about saying no, after all, and Ian Paisley had built his party and career on his ability to conjure the genie of Protestant resistance to any hint of accommodation with the Catholic minority.

But the signs were there all along that he was never quite the politician you thought - especially if your view was based on the roaring demagogue caricatured by Spitting Image.

He talks of his profound faith with humility and simplicity for example, he is a sophisticated operator at Westminster and he has always been capable of surprising geniality.

'Defined by hostility'

Why has he changed?

Well, in part, he has mellowed with age.

And of course, by definition he is the first unionist leader in 40 years who has not been frightened away from the prospect of change by the thought of being denounced in the most lurid of terms by Ian Paisley.

But more than anything perhaps, he has shown the political veteran's sure grasp of the times in which he lives.

Unionism for years has been a reactionary political movement - defined by hostility to Irish unity and to IRA violence.

With IRA violence gone from the picture and the Irish Republic suddenly benign and Protestant-friendly, unionism has had to operate in a changed political landscape.

"Ian Paisley has identified the moment and risen to it"

The old reasons for refusing to cut a deal which Ian Paisley once articulated with such passion and power are largely gone and even in his 80s, Ian Paisley has identified the moment and risen to it.

How different - how statesmanlike - his legacy will be now than it would have been if he had left the stage five years ago.

I should have paid more attention to the friendly small talk in that taxi queue all those years ago.